Pebble heat exchanger



Felb. 26, 1957 R, R, Goms 2,783,097

PEBBLE HEAT EXCHANGER AT TOR N EYS Feb. ze, 1957 R R Goms 2,783,097

PEBBLE HEAT EXCHANGER Filed March 27, 1952 2 Sheets-Shes?I 2 llllll/llIl/llll/IlllIlIlllllllllllllllllllllI/IL INVENTOR. R. R.GO|NS BY M W ATTORNEYS nited States Patent PEBBLE HEAT EXCHANGER Robert R. Goins, Bartlesville, Okla., assignor to Phillips Petroleum Company, al corporation of Delaware Application March 27, 1952, Serial No. 278,837 4 Claims. (Cl. 302-53) This invention relates to pebble heat exchangers. In one of its more specific aspects, it relates to pebble heat exchanger apparatus. In another of its more specific aspects, it relates to an improved means for controlling the movement of pebbles through a pebble heat exchanger. In another of its more specic aspects, it relates to a means for feeding pebbles into a gas lift-type elevator. In another of its more specific aspects, it relates to a method for entraining pebbles in a gas lift-type elevator.

Apparatus of the so-called Pebble Heater type has been utilized in recent years for the purpose of heating iluids to elevated temperatures. Such apparatus is especially suited for use in temperature ranges above those at which the best available high temperature structural alloys fail. Thus, such equipment may be used for superheating steam or other gases and for the pyrolysis of hydrocarbons to produce variable products such as ethyl# ene and acetylene, as well as for other reactions and purposes. Conventional pebble heater-type apparatus includes two refractory lined contacting chambers disposed one above the other and connected by a refractory lined passageway or pebble throat of relatively narrow cross section.

Refractory solids of iowable size and form, called pebbles, are passed continuously and contiguously through the system, ilowing by gravity through the uppermost chamber, the throat, and the lowermost chamber, and are then conveyed to the top of the uppermost chamber to complete the cycle.

` Solid heat exchange material which is conventionally used in pebble heater apparatus is generally called pebbles The term pebbles as used herein denotes any solid refractory material of tlowable size and form, having strength, which is suitable to carry large amounts of heat from the pebble heating chamber to the gas heating chamber wit-hout rapid deterioration or substantial breaking. Pebbles conventionally used in pebble heater apparatus are ordinarily substantially spherical in shape and range from about 1/3 inchto about l inch in diameter. In a high temperature process, pebbles having a diameter of between 1A to 3%: inch are preferred. The

pebbles must be formed of a refractory material which will withstand temperatures at least as high as the highest temperature attained inthe pebble heating chamber. The pebbles must also be capable of withstanding temperature changes within the apparatus. Refractory materials, such as metal alloys, ceramics, or other satisfactory material may be utilized to form such pebbles. Silicon carbide, alumina, periclase, beryllia, Stellite, zirconia and mullite may be satisfactorily used to form such pebbles or may be used in admixture with each other or with other materials. Pebbles formed of such materials, when properly fired, serve very well in high temperatures, some withstanding temperatures up to about 4000" F. Pebbles which are used may be either inert or catalytic as used in any selected process.

The pebbles are heated in one of the chambers (prefer- ICC ably the upper one) by direct contact therein with hot gases, usually combustion products, to temperatures generally in the range of 1400 F. to 3200 F. The hot pebbles are thereafter contacted with the fluid to be superheated or reacted, as the case may be, in the other chamber. Generally, pebble inlet temperatures in the second chamber are about 50 F. to 200 F. below the highest temperature `of the pebbles within the first chamber. In the process for the production of ethylene from light hydrocarbons, such as ethane, propane, or butane, the pebble temperature in the reaction chamber is usually in the range of 1200 F. to 1800 F. For the production of acetylene by pyrolysis of hydrocarbons, temperatures in the range of 1600 F. to 3000 F. are desirable.

In the past, considerable trouble has been encountered in removing a uniform feed Vof pebbles from the lower end portion of a pebble heat exchanger. Conventional feeding mechanisms which have been used for providing controlled ilow of pebbles from the lower end portion of pebble heat exchangers include star valves, gate valves, vibratory feeders and rotatable table feeders. These conventional feeders have normally been positioned within the conduit extending between the lower end portion of the lowermost pebble heat exchanger chamber and the pebble elevator. These pebble feeders were initially used in connection with mechanical pebble elevators. More recent practice in pebble heat exchangers has been to utilize a gas lift for the purpose of elevating pebbles to the uppermost pebble heat exchange chamber. Trouble has been encountered, when using the conventional feeders, in obtaining good entrainment of the pebbles without subjecting those pebbles to considerable mechanical shock. during the initial entrainment thereof. I have devised a means whereby a closer control `of pebble ilow is obtained with a smaller amount of mechanical shock to the pebbles. Control of pebble flow in this manner unexpectedly reduces abrasion of the conduit extending between the reaction chamber and the gas lift.

At least one of the following objects of the invention isattained by at least one aspect of this invention.

An object of this invention is to provide improved pebble heat exchange apparatus, Another object of the invention is to provide improved pebble feeding means. Another object of the invention is to provide means for controlling the volume flow of pebbles to a pebble elevator. Another object of the invention is to provide means for entraining pebbles in a gas lift-type elevator with a minimum of mechanical shock to the pebbles. Another object of the invention is to provide an improved method for entraining pebbles in a gas lift-type elevator. Other and further objects and advantages will be apparent to those skilled in the art upon study of the accompanying discussion and the drawings.

Broadly speaking, this invention comprises introducing pebbles into an upilowing stream of lift gas from points about the entire circumference of the lift-gas conduit. The lift gas is introduced into the bottom portion of the lift-gas conduit and passes upwardly therethrough. Pebbles are passed from the pebble heat exchange chamber into a circumferential chamber surrounding the gaslift conduit. Pebbles are introduced into the gas stream at a controlled rate from the circumference of the gaslift conduit thereby providing a more uniform introduce tion of pebbles into the gas stream and materially reducing the contact between pebbles and between pebbles and the gas-lift conduit. In this manner the mechanical shock to which the pebbles are subjected is materially reduced when compared to conventional methods of operation. The pebbles ilowing into the gas lift have less energy and for that reason the pressure drop through the gas lift is less than encountered in conventional units.

Better understanding of this invention will be obtained upon study of the accompanying schematic drawings in which Figure l is a diagrammatic .representation of a pebble heat exchanger system. Figure 2 is a preferred form of the pebble feeding device of this' invention. Fig ure 3 is another modification of the pebble feeding device of this invention. Figure 4 is another modification of the pebble feeding device of this invention. Figure 5 is yet another modification of the pebble feeding device of this invention.

Referring particularly to Figure l of the drawings, upright elongated shell 11 is closed at its upper and lower ends by closure members 12 and 13, respectively. Pebble inlet means 14 may be a single conduit, as shown, or may be a plurality of pebble conduits connected to the upper end portion of shell 11 at separated points. Gaseous eilluent outlet conduit 15 is provided in the upper end por tion of shell 11, preferably extending from closure inember 12. Gaseous inlet conduit 16 is connected to the lower end portion of shell 11, preferably through closure member 13.

Upright elongated shell 17, closed at its upper and lower ends by closure members 1S and 19, respectively, is disposed below shell 1l and the upper end portion of shell 17 is connected to the lower end portion of shell 11 by pebble conduit means such as conduit20 or by a plurality of such conduits. An inert gas inlet conduit is connected to conduit 20 intermediate its ends. Gaseous euent conduit 22 extends from the upper end portion of shell 17 and gaseous material inlet conduit 23 is connected to the lower end portion of shell 17, preferably through closure member 19. Pebble outlet conduit 24 extends downwardly from the lower end portion of shell 17 and is connected at its lower end portion to pebble feeder assembly 25. Pebble feeder assembly 25 surrounds a lower end portion of elevator conduit 26 and communicates with said elevator about the circnmfer ence of the elevator conduit. Gas-pebble separator charnber 27 encompasses the upper end portion of elevator conduit 26 and is connected at its lower end portion to the upper` end portion of pebble inlet conduit 14. Gaseous material outlet conduit 23 extends from the upper end portion of the gas-pebble separator chamber 27. Lift-gas inlet conduit 29 extends into the lower end of elevator conduit 26.

Specific details of pebble feeder 25 are set forth in Figures 2, 3, 4 and 5. Referring to Figure 2, pebble feeder 25 comprises an outer casing 31 which is connectedl at its upper end portion to pebble conduit 24. The lower end portion of shell 31 is formed as a `hopper 32. Elevator conduit 26 extends longitudinally through shell 31 and is provided in the portion of the conduit within the bottom section of shell 31 with a plurality of slots 33 longitudinally disposed with respect to conduit 26. Slots 33 are preferably rectangular in shape and generally range between l and 31/2 inches in width and between 2 and 15 inches in length. At least 2, preferably more than 6, of these slots are utilized and are disposed about the circumference of thc elevator conduit. Surrounding a portion of elevator conduit 26 within shell 31 is a sleeve 34 which is movable longitudinally with respect to the elevator conduit. A pinion gear 35 is diagrammatically shown as a means for moving sleeve 34 longitudinally along elevator conduit 26. Pinion 35 is connected to a drive means, not shown. Other actuating means than the pinion may be used for elevating or lowering sleeve 34. That actuation can be by ratchets or threaded connections with drive means if so desired. Sleeve 34 surroundsclevator conduit 26 and when lowered, progres sively closes `a portion of each of the slots 33 so as to reduce the area of the opening through each of the slots. Conduit 29 is connected to the lower end portion of con duit 26 for the introduction of lift gas thereinto.

ln the operation of the device shown in Figure 2,

. tween conduits 26 and 26'.

pebbles are introduced into the pebble feeder 25 through conduit 24. The pebbles gravitatc downwardly and across the chamber formed within shell 31 so as to form an annular pebble mass around sleeve 34 and elevator conduit 25. A lift gas is introduced into the lower end portion of elevator conduit 26 through inlet conduit 29. The lift gas passes upwardly through elevator conduit 26 past the Openings of slots 33. The pebbles gravtatc downwardly as an annular mass and into the elevator conduit 26 through `the plurality of openings formed by slots 33. The tlow of pebbles into elevator conduit 26 is relatively uniform and is closely controlled by raising or lowering sleeve 34. The gases sweeping upwardly across the openings of slots 33 immediately entrain thc pebbles as they gravitate through those openings, thereby obviuting thc problem of .mechanical shock which has been a serious problem in the operation of gas lifbtypc elevators to the present time.

Referring particularly to the device shown as Figure 3 of the drawings, pebble feeder 25' comprises au upright shell 36 which is closed at its ends and is provided with elevator conduit 26 extending centrally through the upper end thereof downwardly to an intermediate level within said shell. A lower end portion of elevator conduit 26 shown as 26 extends upwardly into shell 35 to a point im mediately below conduit 2d and is rotatably mounted in the lower end of shell 36 by means of support-bearing 37. Intermediate shell 33 extends downwardly from the upper end of shell 36 to substantially the same level as the lower end of elevator conduit 2.6. Pebble conduit 24 extends into the upper end portion of the chamber formed between shell 38 and elevator conduit 26. The lower end of elevator conduit 26 is belled, or of larger diameter than conduit section 26 so as to facilitate the entrainment of pebbles directly into conduit 26. A table 39 having an upwardly extending peripheral lip 4l is rigidly connected to the upper end portion of conduit section 26' and rotates with the latter conduit. Peripheral lip 41 is preferably larger in diameter than intermediate chamber 38 and extends upwardly to a point at least as high as the lower end of intermediate shell 38. Rotating means, such as a gear wheel 42, and drive means, such as motor 43, are diagrammatically shown for the purpose of rotating the conduit section 26. Other types of drive means and connecting means which are conventional can be utilized for rotating the conduit section 26 and its connected table 39. Conduit 26 is spaced from the lower end of conduit 26 a distance sufficient to permit pebbles to flow into the interior of conduit section 26. Conduit section 26 preferably extends slightly through the center of table 39, though this extension or lip is not a necessity in the operation of this device. Lift-gas inlet conduit Z9 is connected to the lower end portion of conduit section 26 by means of a seal member 44. Seal member 44 provides a means whereby conduit section 26 is permitted to rotate while a gas-tight seal is maintained at zthe lower end of the conduit. Seals such as seal 44 are conventional in the art and need not be more fully described herein.

The operation of 4the pebble heat exchanger of this invention utilizing the pebble feeder shown in Figure 3 is somewhat similar to that which is disclosed in connection with Figure 2. Pebbles gravitatc into peeble feeder 25 through conduit 24. The pebbles are maintained as an annular pebble bed between intermediate shell 38 and elevator conduit 26. The annular mass of pebbles graviitates downwardly to the end of conduit 26 and is supported upon rotatable table 39 which is in turn connected to conduit section 26'. Conduit section 26 is rotated at a speed such that pebbles are displaced from their normal position and are caused to fall into the opening between conduit 25 and 26. Lift gas is introduced into the lower end portion of conduit section 26 and 'flows upwardly through that conduit past the opening be- Pebbles which fall through the opening between4 these two conduits are entrained in Ithe gas flow and are elevated to separator chamber 27, shown in Figure l wherein the gas and pebbles are separated. The pebbles gravitate into the upper end portion of shell 11 and the gas is exhausted from chamber 27 through outlet conduit 28. The speed at which table 39 is rotated can be manually ,controlled or can be automatically controlled in response to the volume of pebbles entrained in the lift gas or in Iresponse to the level of. pebbles within chamber 11 or in response to other similar conventional measurements.

Referring particularly to the device shown in Figure 4 of the drawings, it will be noted that thisdevice is much the same as that shown anddescribed as Figure 3 except for the fact that conduit section 26 is movable longitu dinally, together with table 39. .Table 39 is supported on a plurality of rollers 45 which are in turn supported by means such -as annular support member 46. Support member 46 rests upona plurality of adjusting members such as bolts 47. Bolts 47 are threadedly connected to the lower end portion of shell 36. When bolts 47 are screwed upwardly into the interior of shell 36 support member 46' and rollers 45 are also displaced upwardly, thereby mov# ing table 39 and conduit section 26 upwardly in the chamber. Motor 43 is" adjustably mounted on bracket member 48 so that it also can be raised and lowered to correspond with the level of the conduit section 26. Connection with conduit section 26 is made through gear wheel 42. Upward movement of conduit section 26 narrows the opening between conduits 26 and 26', thus reducing the pebble ow obtained through the opening therebetween. When conduit section 26 is lowered, the opening is enlarged and the upper end of conduit section 26' is dropped further below the normal angle of repose of the pebbles thereby permitting free gravitational flow of pebblesY into the opening between conduits 26 and 26. Adjustment of the height of conduit section 26' and table 39 is made in accordance with the volume of pebbles which it is desired to move through elevator conduit 26.

Although the adjustment of the height of table 39 and conduit section 26 would be made manually with the specific device schematically shown in Figure 4, it is obvious that each of the bolts could be provided with a pulley and a common drive means attached thereto. The raising or lowering of conduit section 26 and table 39 can also be accomplished by placing the elevating mech- -anism in connection with conduit section 26 outside of shell 36. This could be done by rigidly fastening a ange about the circumference of conduit section 26' and placing elevating mechanism in operative connection with such a flange.

Referring particularly to the device shown in Figure 5 of the drawing it will be noted that this device is very similar to the device shown in Figure 2 of the drawings. Pebble feeder 25 comprises an upright, elongated, closed shell 31 provided with pebble inlet means 24 in the upper end portion thereof. Elevator conduit 26 extends downwardly to an intermediate level within the chamber formed by shell 31. Conduit section 26 extends upwardly into the chamber formed within shell 31 and is positioned in line with conduit 26. The upper end of conduit 26 is positioned on a level some distance below conduit 26, particularly below a level from which an inverted cone, having its vertex in the upper end of conduit section 26' would intersect the lower end of conduit 26, the sides of that inverted cone deviating from the horizontal by substantially the angle of repose of pebbles. Sleeve member 49 is positioned within the lower end portion of conduit 26 and is provided with a gear race 51 longitudinally positioned on its outer surface. Gear race 51 is positioned within a slot 52 formed in the lower end portion of conduit 26 and is moved by pinion gear 53, motivated by independent drive means, not shown. Slot 52 and pinion gear 53 are encased within casing member 54 so as to prevent pebbles from becoming enmeshed between gear race 51 and pinion member f 53. Lift gas inlet conduit end of conduit section 26. Sleeve member 49 can be positioned in the upper end of conduit section 26' if so desired.

The operation of the pebble feeder shown as Figure 5 of the drawings is very similar to that shown as Figure 2. The elevator conduit has been formed as two sections so as to provide a continuous opening therebetween and to permit a greater volume of pebbles to ow into that conduit. Control of pebble ow is obtained by lowering or raising sleeve member 49 so as to narrow or enlarge the opening between that'sleeve member and conduit section 26. When sleeve member 49 is lowered it tends to intersect the imaginary inverted cone, the sides of which deviate from the horizontal by the angle of pebble repose, when that cone has its vertex positioned in the axis and at the upper end of conduit section 26. v

In each of the pebble feeders described hereinabove, the pebbles are fed into the elevator conduit from points about the entirel circumference of that conduit. ventional practice, wherein the single pebble conduit extends into the elevator conduit it is common practice to use secondary entraining gas so as to cause the pebbles -to iiow into the elevator conduit. In such practice, slugs of pebbles have been caused to move rapidly into the elevator conduit and were impinged against the surface of the elevator conduit and of other pebbles, thereby imposing considerable mechanical shock upon the pebbles. My invention utilizes a head of contiguous pebbles formed within the pebble feeder chamber and those pebbles are uniformly moved into the elevator conduit from about its circumference. In the modification shown in Figures 3 and 4, this head of pebbles is supplemented in motivating force by the rotation of a table feeder which tends to displace the pebbles so as to permit them to move more freely. The pebbles are moved into the elevator conduit from points around the entire circumference of that conduit thereby permitting the entrainment of large amounts of pebbles without causing any one portion of the peb bles to be moved into the gas stream as a very large mass. This greatly simplifies the problem of entrainment of the pebbles. Control of the ow of pebbles is obtained in three ways in connection with the feeder modification of this invention. In the modification of Figures 2 and 5 control is obtained by opening or closing the slots in the elevator conduit to a different degree. In the modilication shown in Figures 3 and 4, control is obtained in the speed of rotation of the table 39. In the modication shown in Figure 4, additional control is obtained by elevating or lowering the table and conduit section 26 so as to reduce the angle between the top of conduit section 26 and the bottom of conduit 26 or to increase that angle so as to decrease or increase the ability of the pebbles to freely gravitate into conduit section 26.

Various modifications of this invention will be apparent to those skilled in the art upon study of the accompanying disclosure. Various means may be used for rotating conduit section 26 and its connected table 39 and similarly various means can be used for elevating or lowerng section 26 and its connectedtable 39. Such modifications are believed to be clearly within the skill of the art and thus within the spirit and the scope of this disclosure.

I claim:

l. An improved pebble heat exchange system comprising in combination a rst closed, upright, elongated pebble chamber having pebble inlet means and gaseous efliuent means in its upper end portion and iluid inlet means in its lower end portion; a second closed, upright, elongated pebble chamber disposed below said iirst chamber and having gaseous effluent means in its upper end portion and fluid inlet means and pebble :outlet means in its lower end; pebble conduit means connecting the lower end of said first chamber and the upper end of said second chamber; a gas-pebble separator chamber connected at 29 is connected to the lower' In cona its lower end portion to the upper end of said pebble inlet conduit to said first chamber; an upright gas lift conduit of fixed length encompassed at its upper end by said gas-pebble separator chamber; a pebble feeder chamber enclosing a lower portion of said gas lift conduit, said pebble feeder chamber being connected at its upper end portion to the lower end of said pebble outlet means; inlet means disposed around the periphery of said gas lift conduit within the lower end portion ofsaid pebble feeder chamber; a sleeve surrounding said gas lift conduit and adapted Ito slide longitudinally thereon, the upper end of said sleeve being in all positions above the connection of said pebble feeder chamber tosaid pebble outlet means and the lower end of said sleeve being adjacent said inlet means; drive means operatively connected to said sleeve above the `connection of said pebbleifeeder chamber to said pebble outlet means so as to move said sleeve and thus vary the area through said inlet means into the interior of said gas lift conduit; and lift gas inlet means connected to the lower end of said gas lift conduit.

2. Au improved pebble feeder comprising in combination a closed, upright shell; pebble inlet means in the` upper end portion of said shell; elevator conduit means of fixed length extending longitudinally through said shell; pebble inlet means in said elevator conduit means in the lower end portion of the chamber formed by said shell and extending through and about the circumference of said elevator conduit means; a `sleeve slidably positioned on said elevator conduit means within said chamber and adjacent said pebble inlet means in said elevator conduit means, the upper end of said sleeve being in all positions above said pebble inlet means; drive means operatively connected to said sleeve so as to move said sleeve and thus vary the area through said pebble inlet means into the interior of said elevator conduit means, said drive means being positioned above said pebble inlet means; and lift gas inlet means connected to the lower end portion of said elevator conduit.

3. An improved pebble feeder comprising, in combination, a closed upright shell; pebble inlet means in the upper end portion of said shell; an elevator conduit of fixed length extending longitudinally through said shell; a pluralityv of slots formed in the lower portion of said elevator conduit and disposed longitudinally about the circumference of said conduit, said slots being of a greater length than width; a sleeve member cooperating with said slots for varying the area of said slots open to pebble ow, the upper end of said sleeve being disposed above said pebble inletmeans; and lift gas inlet means connected to the llower end portion of said elevator conduit.

4. An improved pebble feeder comprising, in combination, a closed upright shell; pebble inlet means in the upper end portion of said shell; an elevator conduit of fixed length extending longitudinally through said shell; a plurality of slots formed in the lower portion of said elevator conduit and disposed longitudinally about the circumference of said conduit; a sleeve member cooper ating with said slots for varying the area of said slots open to pebble iiow, the upper end of said sleeve being disposed above said pebble inlet means; and lift gas inlet means connected .to the lower end portion of said elevator conduit.

References Cited in the ile of this patent UNITED STATES PATENTS 168,029 Korting Sept. 2l, 1875 496,684 Griscom May 2, 1893 528,419 Duckham Oct. 30, 1894 925,591 Pagborn June 22, 1909 1,319,193 Von Porat Oct. 21, 1919 2,412,152 Huff Dec. 3, 1946 2,433,726 Angell Dec. 30, 1947 2,542,887 Watson Feb. 20, 1951 2,561,771 Ardern July 24, 1951 2,630,352 Degnen Mar. 3, 1953 2,649,340 Weinrich Aug. 18, 1953 2,697,685 Fahnestock Dec. 2l, 1954 2,711,350 Delaplaine June 21, 1955 

